The Underneather
Years ago I collected all my "monster feelings" (the intuitive ideas about those things under the bed) and wrote a story called "The Underneather". As I wrote it, I realized there were a lot of "rules": like they can't get you if you hold perfectly still and hold your breath as if you were dead. (Wonder what the monsters thought of the false high child mortality rate in my neighborhood?)
I recall a frightening collary to the "can't get you if most of you is under the covers" bit. My mother tucked in the edges of my blanket so hard, when I hopped in bed at night and pulled it up to my chin, I didn't pull it closer so much as stretch it. So I'd wake up in the middle of the night feeling the blanket creep down ever so slowly from my upper chest. "They" were trying to get around the "under the covers" rule in an evil, crafty fashion! I set my little fists like cement over the upper edge of the blanket (naturally, if I seized the covers and dragged them up, they'd see I was awake).
Sometimes I'd wake up, eyes still closed, and feel sure that if I opened my eyes, I'd be staring right into the ogling orbs of a flesh-eating Thing only inches away. So I kept my lids shut tight and tried to breathe regularly, as if still asleep.
Yes, the wondrous days (and nights) of youth!
Oh -- in my story, there's a rule that "they" can move around your room and play with your toys, but they can't leave any evidence for daylight, so everything's always back where it was the night before. But one day young Tim wakes to find all his clothing and books and toys piled in a single mound in the middle of the floor . . .